The heart of a computer is a magnetic hard disk drive (HDD) which typically includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and/or write heads over selected data tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The volume of information processing in the information age is increasing rapidly. In particular, it is desired that HDDs be able to store more information in their limited area and volume. A technical approach to meeting this desire is to increase the capacity by increasing the recording density of the HDD. To achieve higher recording density, further miniaturization of recording bits is effective, which in turn typically requires the design of smaller and smaller components.
The further miniaturization of the various components, however, presents its own set of challenges and obstacles. For instance, the ongoing push for higher storage bit densities in magnetic media used in disk drives has reduced the size (volume) of data cells to the point where the cell dimensions are limited by the grain size of the magnetic material. Although grain size can be reduced further, there is concern that data stored within the cells is no longer thermally stable, as random thermal fluctuations at ambient temperatures are sufficient to erase data. This state is described as the superparamagnetic limit, and occurs where the average thermal energy (kBT) within the grain becomes proportional to the magnetic anisotropy energy (KuV), where kB is Boltzmann's constant, T is the absolute temperature, Ku is the magnetic anisotropy constant of the grain, and V is the volume of the grain. Conventional magnetic recording media are thus limited to about 1 Terabit per square inch due to the limited magnetic anisotropy energy (KuV) of current Co—Cr based materials (e.g., CoCrPt).
The superparamagnetic limit may be raised by increasing the coercivity of the magnetic media or lowering the temperature. Lowering the temperature may not be practical when designing hard disk drives for commercial and consumer use. Raising the magnetic anisotropy (and thus the coercivity) of the media, on the other hand, may exceed the write field capability of the write head.
Several techniques, such as heat assisted magnetic recording (HAMR) and microwave assisted magnetic recording (MAMR), have emerged to address the difficulty in maintaining both the thermal stability and write-ability of the magnetic media. For instance, HAMR employs heat to lower the effective coercivity of the magnetic media used to store data, whereas MAMR employs a high-frequency oscillating magnetic field (in addition to a recording magnetic field emanated from a main pole of the write element) to lower the effective coercivity of said media. However, current materials having a magnetic anisotropy (e.g., FePt), which may be particularly useful in HAMR and MAMR applications, have not been shown to exceed current Co—Cr based media in terms of recording capability.
Ferroelectric recording media has also garnered recent interest. Ferroelectric materials store information in the form of the upward or downward electric polarization direction of individual domains. While ferroelectric recording media are capable of storing data at very high areal densities, problems exist with respect to current methods for recovering the stored information (i.e., current readback mechanisms). For instance, screening charges (e.g., electrons or ions) located at the surface or at interfaces between a ferroelectric layer and adjacent layers in a ferroelectric recording medium may cancel external electric fields, which may enhance the stability of the medium for data storage but also complicate the readback process. There is thus a need in the art for an improved system and/or method of reading back information stored on ferroelectric recording media.